The present disclosure relates to ink-jet printing, particularly involving phase-change ink printing directly on a substrate, wherein the substrate can be a substantially continuous web or can be a substrate such as paper or cut paper. In embodiments, the printing apparatus includes an ink spreader station having an ink spreader member, which may be heated, and a back-up pressure member. In embodiments, the pressure member of the ink spreader/pressure system includes a conductive surface, or surfaces, comprising single or multiple layers of polymers like polyurethanes, silicones, ethylene propylene dienemethylene terpolymer, nitrile butadiene rubber, and the like, and combinations thereof.
In further embodiments, the conductivity in these surface(s) can be imparted by the addition of ionic salts, electronically conducting particles, or the like, or combinations thereof.
Ink jet printing involves ejecting ink droplets from orifices in a print head onto a receiving surface to form an image. The image is made up of a grid-like pattern of potential drop locations, commonly referred to as pixels. The resolution of the image is expressed by the number of ink drops or dots per inch (dpi), with common resolutions being 300 dpi and 600 dpi.
Ink-jet printing systems commonly use either a direct printing or offset printing architecture. In a typical direct printing system, ink is ejected from jets in the print head directly onto the final receiving web or substrate such as paper or cut paper. In an offset printing system, the image is formed on an intermediate transfer surface and subsequently transferred to the final receiving web. The intermediate transfer surface may take the form of a liquid layer that is applied to a support surface, such as a drum. The print head jets the ink onto the intermediate transfer surface to form an ink image thereon. Once the ink image has been fully deposited, the final receiving web is then brought into contact with the intermediate transfer surface and the ink image is transferred to the final receiving web.
U.S. Pat. No. 5,389,958 is an example of an indirect or offset printing architecture that uses phase change ink. The ink is applied to an intermediate transfer surface in molten form, having been melted from its solid form. The ink image solidifies on the liquid intermediate transfer surface by cooling to a malleable solid intermediate state as the drum continues to rotate. When the imaging has been completed, a transfer roller is moved into contact with the drum to form a pressurized transfer nip between the roller and the curved surface of the intermediate transfer surface/drum. A final receiving web, such as a sheet of media, is then fed into the transfer nip and the ink image is transferred to the final receiving web.
U.S. Pat. Nos. 5,777,650; 6,494,570; and 6,113,231 show the application of pressure to ink-jet-printed images. U.S. Pat. Nos. 5,345,863; 5,406,315; 5,793,398; 6,361,230; and 6,485,140 describe continuous-web ink-jet printing systems.
U.S. Pat. No. 5,195,430 discloses a pressure fixing apparatus for ink jet inks having 1) an outer shell of rigid, non-compliant material such as steel, or polymer such as acetal homopolymer or Nylon 6/6, and 2) an underlayer of elastomer material having a hardness of about 30 to 60, or about 50 to 60, which can be polyurethane (VIBRATHANE, or REN:C:O-thane).
U.S. Pat. No. 5,502,476 teaches a pressure roller having a metallic core with elastomer coating such as silicones, urethanes, nitrites, or EPDM, and an intermediate transfer member surface of liquid, which can be water, fluorinated oils, glycol, surfactants, mineral oil, silicone oil, functional oils such as mercapto silicone oils or fluorinated silicone oils or the like, or combinations thereof.
U.S. Pat. No. 5,808,645 discloses a transfer roller having a metallic core with elastomer covering of silicone, urethanes, nitrites, and EPDM.
U.S. Patent Publication No. 20030235838 discloses an offset printing machine having an imaging member with an outer coating that may comprise a polyurethane thermoset.
U.S. Patent Publication No. 20060038869 discloses an offset printing machine having an imaging member with an outer coating that may comprise a polyurethane thermoset.
U.S. Patent Publication No. 20060238586 discloses an offset printing apparatus having a transfix pressure member with a substrate and an outer layer having a polyurethane material and positioned on the substrate, wherein the polyurethane outer layer has a modulus of from about 8 to about 300 Mpa, a thickness of from about 0.3 to about 10 mm, and wherein the pressure exerted at the nip is from about 750 to about 4,000 psi, and wherein the outer layer has a convex crown.
Duplex print quality has been a challenging technology issue in many solid ink jet printers. The currently established approach for improving duplex print quality in conventional solid ink print processes is to slow down the duplex speed. Other software modifications have been used, such as the roll on/roll off transfix roll engage/disengage protocol employed in some machines.
Also, of particular concern with direct-to-paper (or direct-on-web) printing is the potential for gloss patterns (ghosting) to be created when the printed side of the paper contacts the pressure roller during duplex. When the ink comes in contact with the pressure roller, some of the oil that is in the ink from the simplex spreading step, transfers to the pressure roller in the pattern of the image. When the oil patterned pressure roller comes in contact with the ink on the page 1 revolution later, it can create gloss patterns called “ghosting.” In the solid ink jet offset process, the transfix roller is oiled via contact with the drum to help minimize this problem. The change in the surface roughness of the ink causing the gloss pattern roller ghosting is believed to be associated with the release or surface properties of the elastomer on the pressure roller or transfix roller. In direct-to-paper processing, there is no contact with the drum since it is a web process.
Accordingly, it is desired to provide a pressure member for use with phase change ink printing machines, including duplex machines and direct-on-paper, direct-on-web, or continuous web machines, which has the ability to assist in the spreading of the direct-on-paper developed print without causing alteration to the previously printed ink that contacts the pressure roll during duplex printing. In particular, it is desired to improve the problem of gloss alterations to the image that can be overall or patterned (ghosting), and ink offset to the pressure roll surface, which can be re-deposited back onto the paper/web. It is desired that the pressure roller maintain the functional properties required for roll performance, while satisfying the electrical conductivity or static dissipation requirements. It is also desired that the pressure member, when heated, be thermally stable when heated to the operating temperature. Moreover, it is desired to provide a pressure roller that is wear-resistant, has consistent mechanical properties under high load, resists adhesion of ink, and is conductive.